The blending of steam with cold water to provide a supply of hot water is commonly used in the food processing industry where there is a frequent need to wash equipment with hot water at a temperature sufficient to clean the equipment. Such food processing applications typically involve the use of a hot water hose gun that is supplied with hot water from a mixing valve. These hot water hose guns generally use a flow on/off trigger for starting and stopping a draw of hot water from the mixing valve and also include means for adjusting the spray pattern.
Thermostatic mixing valves are often used to provide the hot water supply to the hose gun. These mixing valves employ a proportioning valve responsive to the hot water temperature for controlling both the steam and the cold water flow so as to maintain the temperature of the hot water substantially constant. One disadvantage of these types of valves is the inability of known designs to completely shut-off steam flow when the water is turned off. The incomplete shut-off of steam can result in the next draw-off of hot water to start with a violent burst of steam, which can be dangerous. Additionally, known valves are noisy in operation due to the continuous succession of steam implosions that occur when the steam and cold water mixes together in an internal mixing chamber.
Attempts have been made in the prior art to overcome the disadvantages noted above. For example, U.S. Pat. No. 4,834,130 to North teaches a mixing valve that operates based upon pressure differentials within the valve body to minimize steam implosions and provide a complete shut-off of the steam supply. The disclosure of U.S. Pat. No. 4,834,130 is herein incorporated by reference in its entirety.
In addition to the disadvantages noted above, another disadvantage of known mixing valve configurations is premature wear on various components of the mixing valve. This wear occurs due to an excessive amount of heat transfer between the steam inlet portion of the valve and the flow mixing and control components of the valve. This heat transfer can lead to the premature deterioration of the flow mixing and/or control components of the valve, hence leading to both the disadvantages discussed above as well as the possibility of premature failure of the mixing valve.
It is an object of the present invention to provide a mixing valve for mixing steam and water which mitigates at least some of the disadvantages of thermostatic mixing valves discussed above.